Synthetic protein-acidic phospholipid complexes are being used to (1) define the mechanism of calculus calcification and (2) develop an assay for screening potential anticalculus agents. Kinetic studies using a lysozyme-phosphoinositide complex have shown that there is a rapid initial binding of calcium equivalent to 10 microgm/mg of complex which remains constant during the first 24 hours of incubation in a metastable calcium phosphate solution at 37C. The initial calcium binding is followed by a slower uptake of both Ca and HPO4 probably as an intermediate amorphous calcium phosphate phase and finally hydroxyapatite formation after 72 hours of incubation. Once reliable kinetic data are obtained, the mode of action of various inhibitors will be evaluated. The procedure will allow us to determine whether inhibitors block initial calcium binding, interfere with formation of the amorphous intermediate phase or inhibits hydroxyapatite formation. Preliminary studies have shown that chlorotetracycline and diphosphoglyceric acid are effective inhibitors. Similar data are also being obtained for calcifiable proteolipids isolated from microorganisms and vertebrate tissues. These correlative studies could provide valuable information for illucidating the mechanism of biologic calcification.